Do Soil Amendments have a Significant Influence on Element Accumulation in Plant Organs? A Meta-analysis

Abstract Soil amendments generally impact overall soil health and phytoremediation strategies; however, their effects on element accumulation vary and are inconsistent. This meta-analysis examined data from nine independent studies published between 1975 and 2024 to assess how amendments such as manure, sewage sludge, compost, biochar, peat moss, and lime influence metal accumulation in plants compared to plants grown in unamended soils. Hedges’ g values were calculated using a random effects model to compare metal accumulation related to amendment use. Additionally, linear regression analysis evaluated how pH and exposure time affect element accumulation. Results showed that amendments significantly reduced overall plant accumulation of As ( p < 0.001), Cd ( p < 0.001), Cr ( p = 0.005), Cu ( p = 0.004), Pb ( p < 0.001), and Zn ( p = 0.013). For the plant-organ comparison, only root arsenic concentrations were significantly lowered by amendments. Exposure time was positively correlated with the accumulation of Cd, Cu, Mn, Ni, Pb, and Zn in whole plants during amendment application. Regarding pH, higher levels increased root arsenic concentrations but decreased levels of Cd, Cr, and Ni in leaves and roots, as well as Cu in leaves, and Mn and Pb in roots. In conclusion, although amendments can reduce overall plant metal accumulation, this effect is influenced by multiple factors; exposure time, soil pH, and other variables such as amendment type and decomposition stage, all affect metal mobility in various ways and account for the high variability observed across studies.